1. Field of the Invention
The present invention relates to the field of free piston engines and power trains therefore.
2. Prior Art
Internal combustion engines are useful devices for converting chemical energy to mechanical energy by combustion. Typical internal combustion engines convert the energy in petrochemical fuels such as gasoline or diesel fuel to rotary mechanical energy by using the pressure created by confined combustion to force a piston downward as the combustion gases expand and to convert that motion into a rotary motion by use of a crankshaft. However, the use of the piston and crankshaft mechanism introduces many constraints in the operation of the engine that limit the amount of useful mechanical energy that can be extracted from the combustion process.
Free piston engines are linear, “crankless” internal combustion engines, in which the piston motion is not controlled by a crankshaft but is determined by the interaction of forces from the combustion chamber gases, a rebound device and a load device. Hydraulic free piston engines couple the combustion piston to a hydraulic cylinder that acts as both the load and rebound device using a hydraulic control system. This gives the unit operational flexibility. While forms of hydraulic free piston engines in the prior art have achieved good operational flexibility, it would be desirable to provide a hydraulic free piston engine with even greater operational flexibility and energy efficiency.